1. Field
The following description relates to an envelope-tracking current bias circuit capable of being used in a power amplifying system.
2. Description of Related Art
In general, average power tracking (APT) or envelope tracking (ET) may be used as a method of reducing current consumption of a power amplifier module (PAM).
APT is a method of improving efficiency by controlling VCC depending on average output power, while ET is a method of changing a power supply voltage of a power amplifier (PA) depending on an envelope of a radio frequency (RF) signal.
ET is a method of lowering the power supply voltage of the PA with respect to a portion having a low amplitude in the RF signal to reduce average current consumption, but raising the power supply voltage of the PA with respect to a portion having a large amplitude in the RF signal to prevent linearity from being deteriorated.
In APT, VCC follows an average value for a predetermined time, while in ET, VCC follows an output instantaneous value. An ET modulator for generating VCC, simultaneously following an envelope signal, is thus separately required.
In addition, an ET bias circuit may be used in order to further reduce current consumption, and an existing ET bias circuit may use a rectifying circuit in order to detect an envelope signal of an input signal.
However, the rectifying circuit may include a plurality of passive elements and rectifying diodes, and in these passive elements and rectifying diodes, a deviation in a value may be generated due to a process deviation. Particularly, in the rectifying diodes, a deviation in a turn-on voltage may be generated due to a process deviation. Therefore, a deviation in a bias current value may be generated.
A main cause of such a process deviation is that a turn-on voltage of the rectifying diode is changed depending on a process, and a technical solution for this problem is required.